The use of mobile devices for data applications has become increasingly popular in recent years. This popularity has led to a corresponding increase in mobile data traffic, which is projected to grow 39-fold from 2009 to 2014. Such growth has created the demand for additional network capacity, motivating network operators to acquire new licensed spectrum. At the same time, it has strained existing mobile networks, necessitating upgrades to their associated access, transport and backhaul infrastructures. Offsetting the costs of these upgrades by increasing revenues from higher traffic volume presents other challenges due to the operator's cost structure and their current charging model for data applications. As a result, operators are driven to adopt new paradigms to decrease their per-byte data costs. One such approach, which is currently attractive to operators, is to offload their mobile data traffic to alternative access networks. Taking this approach assists in mitigating the need of costly radio access and backhaul network upgrades while simultaneously alleviating usage loads on licensed spectrum.
To fully realize the benefits of offloading, the mobile device should either switch to a more optimal access method when it becomes available during a communication session, or alternatively, select the most optimal access method available when initiating a new session. More advanced approaches involve the simultaneous use of multiple access technologies and methods to achieve a more seamless transition between accesses, increase throughput, and improve performance metrics through path diversity. Alternative access network technologies for offloading include Wireless Fidelity (WiFi), based on the IEEE 802.11x standards, which is capable of providing high throughput (e.g., hundreds of Mbps with 802.11n). One current example of using WiFi for offloading mobile data traffic from cellular networks is the 3rd Generation Partnership Project (3GPP). However, 3GPP does not specify all of the steps needed to achieve a seamless heterogeneous, or vertical, handoff between cellular and Wi-Fi.
Another approach is based on collaboration among mobile devices. In this approach, the mobile device discovers what access options are available, determines whether they would provide sufficient performance for the application, and then selects the best one. To do so, the mobile device queries other mobile devices for a variety of information, which it then uses as decision criteria to select an access node (AN) that will provide the best throughput performance. As an example, the information received from the mobile devices may include the received signal strength (RSS) of various ANs. However, an AN's RSS, by itself, may not guarantee that a given AN will provide the best throughput performance, as the throughput performance typically depends on other factors such as interference levels and traffic loads on the AN and its supporting backhaul network. Additionally, the performance metric could be based on other considerations than throughput alone. For example, the performance metric could be based on delay, loss rates, power consumption, etc.
Additionally, certain applications require a short handoff break. But prior to measuring an AN's RSS, the device has to perform scanning operations to discover what ANs are available, which may cause excessive handoff delays. As a result, 3GPP has defined the Access Network Discovery and Selection Function (ANDSF) to help speed up the discovery of available ANs by providing the mobile device with a list of available access. However, the ANDSF database has to be managed by the operator to keep it up to date, which is labor intensive. Furthermore, the ANDSF database can only include ANs known to the network operator. As a result, the mobile device may perform all of the steps necessary to establish a connection with an AN only to find out that it cannot deliver the desired performance. Yet another approach is a handoff from WiFi to cellular, which typically involves setting a communication session on the cellular side, with session setup contributing to the handoff break. However, 3GPP does not specify all of the steps required to accomplish such handoffs.